The present study investigated the electronic and optical properties of a newly synthesized orange-emitting afterglow phosphor, namely Eu: Mg2SnO4, using the full potential linearized augmented plane wave (FP-LAPW) method. To calculate these properties, the generalized gradient (GGA + U) approximation was employed. The results showed that Eu: Mg2SnO4 exhibited a strong optical response in the visible region, thus highlighting its potential as an excellent candidate for various optoelectronic applications. Notably, the material demonstrated a promising band gap of 2 eV (620 nm), specifically in the orange-emitting afterglow phosphor category, while retaining a 3D structure. These findings suggest that Eu: Mg2SnO4 has promising potential for use in various optoelectronic devices.